High-quality, real-time images are critically needed to safely guide and monitor vascular therapeutic procedures, particularly for coronary arteries. Existing ultrasound catheters are not ideal for this application because they are either side-looking or else occupy too much space. A forward-looking annular array is proposed. The array will contain a large central lumen, through which therapeutic devices can pass, and will provide real-time ultrasound imaging of arteries during a therapeutic procedure. The array, which will exploit the unique advantages of polyvinylidene fluoride (PVDF) as the basic sensing material, will image partially and even totally occluded arteries. During Phase I, a simplified catheter will be designed, characterized and used to predict the performance of a complete Phase II system. Characterization will involve electrical tests, beam pattern measurements and imaging of test phantoms and tissue samples.